package java.lang;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * A programmer assertion that the body of the annotated method or constructor does not perform
 * potentially unsafe operations on its varargs parameter. Applying this annotation to a method or
 * constructor suppresses unchecked warnings about a <i>non-reifiable</i> variable arity (vararg)
 * type and suppresses unchecked warnings about parameterized array creation at call sites.
 *
 * <p>
 * In addition to the usage restrictions imposed by its {@link Target @Target} meta-annotation,
 * compilers are required to implement additional usage restrictions on this annotation type; it is
 * a compile-time error if a method or constructor declaration is annotated with a
 * {@code @SafeVarargs} annotation, and either:
 * <ul>
 * <li>the declaration is a fixed arity method or constructor
 *
 * <li>the declaration is a variable arity method that is neither {@code static} nor {@code final}.
 *
 * </ul>
 *
 * <p>
 * Compilers are encouraged to issue warnings when this annotation type is applied to a method or
 * constructor declaration where:
 *
 * <ul>
 *
 * <li>The variable arity parameter has a reifiable element type, which includes primitive types,
 * {@code Object}, and {@code String}. (The unchecked warnings this annotation type suppresses
 * already do not occur for a reifiable element type.)
 *
 * <li>The body of the method or constructor declaration performs potentially unsafe operations,
 * such as an assignment to an element of the variable arity parameter's array that generates an
 * unchecked warning. Some unsafe operations do not trigger an unchecked warning. For example, the
 * aliasing in
 *
 * <blockquote>
 *
 * <pre>
 * &#064;SafeVarargs
 * // Not actually safe!
 * static void m(List&lt;String&gt;... stringLists) {
 * 	Object[] array = stringLists;
 * 	List&lt;Integer&gt; tmpList = Arrays.asList(42);
 * 	array[0] = tmpList; // Semantically invalid, but compiles without warnings
 * 	String s = stringLists[0].get(0); // Oh no, ClassCastException at runtime!
 * }
 * </pre>
 *
 * </blockquote>
 *
 * leads to a {@code ClassCastException} at runtime.
 *
 * <p>
 * Future versions of the platform may mandate compiler errors for such unsafe operations.
 *
 * </ul>
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.CONSTRUCTOR, ElementType.METHOD })
public @interface SafeVarargs {
}